Electrochemical reactions involve the use of an electric current to effect chemical reactions. In a typical arrangement, an anode immersed in an anolyte and a cathode immersed in a catholyte are separated by a membrane, generally an ion exchange membrane. An oxidation reaction takes place at the anode and a reduction reaction takes place at the cathode. For example, with the electrochemical reduction of carbon dioxide, carbon dioxide is reduced to formate and formic acid at the cathode and oxygen is evolved from water at the anode. In some applications, carbon dioxide is introduced into a catholyte compartment through a porous cathode which porous cathode comprises a cathodic catalyst adapted to reduce carbon dioxide to formate and formic acid.
Cathodic and anodic catalysts play important roles in determining what reactions occur at the cathode and at the anode, respectively, as well as the electrolytic efficiency of such reactions. Efficiency is typically measured as Faradaic Efficiency (FE) and is the efficiency with which electrons (charge) are transferred. That is, the percent of the total current that passes through the electrochemical cell that is used to produce the desired product (e.g., formate). In addition, it is desirable to achieve high current density in stable, long-term use. Tin-based cathodic catalysts, which generally exist as tin, tin oxide (II) (SnO), and tin oxide (IV) (SnO2) (collectively, SnOX), have been shown to give good results in the selective electrochemical reduction of carbon dioxide to formate and formic acid. In addition to selectivity to formate and formic acid, desirable characteristics of such tin-based cathodic catalysts include high surface area of the catalyst on the cathode, physical and mechanical stability, high FE, and high and stable current density during operation. Finally, while catalyst activity can be unpredictable and is highly dependent upon structure, morphology, and electrolysis conditions, other post-transition metals such as lead and indium may also be candidates.